Series-fed phased array



United States Patent 3,258,774 SERIES-FED PHASED ARRA Richard R. Kinsey, Cazenovia, N.Y., assignor to General Electric Company, a corporation of New York Filed Dec. 30, 1963, Ser. No. 334,164 8 Claims. (Cl. 343854) This invention relates to phase scanned array antennas and to means for transmitting energy to and from such antennas. In particular, it relates to the combination of feed networks and phase shifters required by antenna arrays for beam steering.

It is well known in the radar and sonar arts that radiating elements may be advantageously employed in linear and planar arrays. Such arrays provide beam forming and beam steering capabilities which, in many ways, are superior to those of mechanically steered antennas.

Known prior art devices which are most closely related to the present invention have included arrays having element feed lines individually connected to couplers, where the couplers are arranged in series in one or more input lines. Also, they have included arrays having the type of feed network wherein each coupler division (or summation) of RF energy undergoes successive coupler divisions (or summations). These prior art devices have been characterized by a number of limitations. Some have been limited to small arrays of narrow bandwidth. Some have presented problems because they reradiate mutually coupled energy as sidelobes. Others have been strictly passive systems with receive beams limited to pointing in fixed directions. In addition, the prior art devices have been of large volume and weight.

It is, therefore, an object of the present invention to provide a serially fed array antenna and scanner system capable of steering a beam of large frequency bandwidth.

It is a further object of the invention to provide a serially fed linear array module capable of rapid beam steering and adaptable to be included in a large planar array.

It is still another object of the invention to provide afeed network system which, in itself, does not introduce changes in the direction of boresight of a beam with variations in frequency of the RF input signal.

It is yet a further object of this invention to provide a feed network in a phased array radar which is more compact and light weight than the prior art devices.

The invention relates to array antennas and to means for steering beams radiating into or out of such antennas. Specifically, the invention requires that individual elements making up each row (or column) of an array antenna be coupled through individual phase shifters and into suitable couplers connected serially in a transmission line. Each transmission line in turn is coupled at its center to a hybrid junction so that signals for transmission to the individual antenna elements may be provided and so that sum and difference monopulse signals can be derived for angle tracking.

Novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawings in which FIG. 1 illustrates a preferred used in most applications of this invention.

3,258,774 Patented June 28, 1966 embodiment of the invention and FIGS. 2, 3 and 4 are provided to show the general construction of particular portions of the embodiment of FIG. 1.

FIG. 1 shows a general arrangement of components which may be made to realize a practical embodiment of the invention. The embodiment shown in FIG. 1 may be called a series-fed linear array system which, when operated as a receiving device, will provide output signals at terminals 2 and 4 which are proportional respectively to the sum and difference of the signals received by the radiating elements comprising the two halves of the linear array illustrated in the figure. The signals representing the sum and difference can be used for monopulse tracking in one plane and the system may be extended to monopulse tracking in the orthogonal plane by combining signals from a number of such linear arrays. When operating in a transit mode, a transmitter at 6 will provide power through a duplexer 8 to the hybrid H and thence to the radiating elements.

The radiating elements R1, R2 RX RN may preferably be slot dipoles, however, they may take any form which will function properly as radiators of signals of the required frequencies. The radiating elements are coupled through suitable microwave transmission lines L1, L2 LN to the phase shifters at P1, P2 PN. These transmission lines may be either TEM lines, such as coax lines, or loaded waveguides, such as ridge waveguides or dielectric filled waveguides.

The phase shifters, as indicated in FIG. 1, are of a kind which may be varied, by means not shown, so that the phase of the radiating elements may be controlled to enable scanning. 'It is anticipated that this invention will be used with a radar system having appropriate computing elements which can determine the proper setting for each of the phase shifters and provide appropriate signals, either mechanical or electrical, to adjust the phase shifters. For applications where high speed is not required mechanically adjusted phase shifters might be used, however, it is expected that electronically variable phase shifters and preferably digital phase shifters will be A suitable digital phase shifter is disclosed in a co-pending patent application filed in the name of Hugh A. Hair entitled Ferromagnetic Phase Shifter, Serial No. 326,582, on November 27, 1963 and assigned to the same assignee as the present invention. The phase shifters are coupled through lines identified as L'l, L'2 LN to suitable cross-guide couplers labelled C1, C2 ON. The crossguide couplers are coupled in ridge waveguides W1 and W2 to form non-resonant linear arrays connected by the hybrid H.

The hybrid H can be a special ridge waveguide hybrid much like a conventional short slot hybrid, or it can be a conventional coax hybrid with coax-to-ridge waveguide transitions. In either case, the hybrid will provide output signals proportional to the sum and difference of the signals received by the radiating elements when it operates in its receive mode and will transmit appropriate signals from the transmitter 6 through the duplexer 8 to the radiating elements when it operates in its transmit mode.

Certain considerations which are important to the construction of an operating device in accordance with the general plan disclosed in FIG. 1 should be made. First of all, it should be noted that in such array radars it is highly desirable to be able to scan a beam over very wide angles. This requirement immediately imposes a restriction on the system requiring that the radiating elements be spaced approximately one-half wavelength apart to avoid forming secondary echelon lobes. This space limitation in turn requires the use of either TEM line such as coax line, or loaded waveguides such as ridge waveguides or dielectric filled waveguides. Of these alternatives, the ridge waveguide is preferable, because of a need for the use of directive cross-guide couplers with rather tight coupling values. It will be appreciated that tight coupling values of the cross-guide couplers will be necessary in order to reduce the power loss in the waster loads T1 at the ends of the feed line W1 and W2 during operation in the transit mode as well as the losses in the terminations T2 during operation in the receive mode. A preference for ridge waveguide can also be expressed because of the capacity of such waveguides to transmit larger amounts of power while at the same time the ridge present in the waveguide lowers the cutoff frequency of the waveguide to permit a wider bandwith to be transmitted.

The symmetry of the array, i.e., the fact that it is fed at its center, offers certain distinct advantages. Connection of the array in the center through a hybrid H. for example, enables the system to directly provide the sum and difference monopulse signals required for angle tracking. Also, it will be noted that with small frequency changes, the symmetry of the array about its center will not change and the bore-sight of the beam will be shifted not at all due to the feed network though the beam may tend to become de-focused as the frequency shifts significantly. It should be noted that a requirement for re-phasing the array with significant changes in frequency, in order to maintain beam pointing direction, is not peculiar to this invention. Rather, this requirement prevails for any feeding scheme wherein the scan computer drops multiples of a wavelength from the phase shifter commands, as is usually the case.

It is possible with an operating device constructed in accordance with FIG. 1 to select values of coupling for each coupler C1 through CN such as to provide a near uniform excitation for maximum gain, or a tapered excitation for reduced sidelobes. In general, coupling must get progressively tighter as the coupling point is located further and further from the hybrid H. In fact it is desirable to obtain a degree of coupling towards the end of the line, as at C1 and C2, which is greater than was thought possible until recently. Coupling apertures which may be used with this invention are shown in FIGS. 2, 3 and 4 where FIGS. 2 and 3 represent prior art slots with FIGS. 3 and 4 showing slots having greater potentials for tight coupling. FIG. 4 is believed to show a novel slot. Reference to suitable coupling means may of the ability of a scan computer to compensate for frequency effects, this invention permits a great reduction in the bulk and weight of feeding structures over the requirements of prior art devices.

It has been previously indicated that a planar array may be constructed from an array of linear arrays and a planar array is commonly treated as made up of an array of linear arrays for that reason. One of the purposes of the present invention is to provide a linear array building block which will permit the realization of a compact, lightweight and efficient planar array feed structure. The

hybrid at the center of each series fed linear array provides sum and difference signals for monopulse tracking in one plane. Monopulse tracking in the orthogonal plane may be obtained by combining the sum and difference signals from all the linear arrays, at either RF or IF frequencies. If each linear array is driven by a separate phase controlled transmitter and is provided with its own receivers, row-column steering can be obtained by incurring the elfective loss of only one phase shifter. Moreover, a stack of beams can be formed at IF in one plane, or the beam shape can be changed.

Although the invention has been described with respect to certain specific embodiments, it will be appreciated that many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention. -It is intended, therefore, that the appended claims shall cover all such modifications and changes as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A beam steering system comprising,

a linear array of radiating elements,

a plurality of phase shifters,

means coupling each of said radiating elements to a first terminal of one of said phase shifters,

a transmisison line,

a plurality of cross-guide couplers arranged serially in said transmission line,

means coupling a second terminal of each of said phase shifters to a separate one of said cross-guide couplers, and

a hybrid junction coupled to the center of said transmission line to deliver signals proportional to the sum and to the difference of signals received by the array elements and transmitted through the phase shifters, the cross-guide couplers, the coupling means and the transmission line.

2. A beam steering system substantially as claimed in claim 1 in which the phase shifters are digital phase shifters.

-3. A beam steering system substantially as claimed in claim 1 in which the cross guide couplers are chosen to provide tighter and tighter coupling the further they are located from the hybrid junction.

4. A beam steering system substantially as claimed in claim 1 in which the cross-guide couplers comprise slotted apertures selected to provide appropriate tightness of coupling at each point of occurrence.

5. A beam steering system comprising,

a linear array of N radiating elements,

a plurality of N phase shifters,

means coupling each of said N radiating elements to a first terminal of a separate phase shifter,

a feed line,

a plurality of N cross-guide couplers arranged serially in said feed line,

means coupling a second terminal of each of said N phase shifters to a separate one of said cross-guide couplers, and

a hybrid junction coupled to the center of said feed line to deliver signals proportional to the sum and to the difference of signals received by the array elements and transmitted successively through the phase shifers, the cross-guide couplers, the coupling means and the feed line.

6. A beam steering system substantially as claimed in claim 5 in which the phase shifters are digital phase shifters.

7. A beam steering system substantially as claimed in claim 5 in which the cross-guide couplers are chosen to provide tighter and tighter coupling the further they are located from the hybrid network.

8. A beam steering system substantially as claimed in claim 5 in which the cross-guide couplers comprise slotted 5 6 apertures selected to provide appropriate tightness of cou- OTHER REFERENCES P each P of occurrence Blass, Multidirectional Antenna, IRE International Convention Record, v01. 8, part 1, 1960, pages 48, 49 References Cited by the Examiner 5 relied on.

UNITED STATES PATENTS HERMAN KARL SAALBACH, Primary Examiner.

2,759,154 8/1956 Smith et a1. 3,090,956 5/1963 Woodward et a1. 3438-54X ELI'LIEBE'RMAN Emmmer- 3,182,325 5/1965 Blume 343-854 X R. F. HUNT, JR., Assistant Examiner. 

1. A BEAM STEERING SYSTEM COMPRISING, A LINEAR ARRAY OF RADIATING ELEMENTS, A PLURALITY OF PHASE SHIFTERS, MEANS COUPLING EACH OF SAID RADIATING ELEMENTS TO A FIRST TERMINAL OF ONE OF SAID PHASE SHIFTERS, A TRANSMISSION LINE, A PLURALITY OF CROSS-GUIDE COUPLERS ARRANGED SERIALLY IN SAID TRANSMISSION LINE, MEANS COUPLING A SECOND TERMINAL OF EACH OF SAID PHASE SHIFTERS TO A SEPARATE ONE OF SAID CROSS-GUIDE COUPLERS, AND A HYBRID JUNCTION COUPLED TO THE CENTER OF SAID TRANSMISSION LINE TO DELIVER SIGNALS PROPORTIONAL TO THE SUM AND TO THE DIFFERENCE OF SIGNALS RECEIVED BY THE ARRAY ELEMENTS AND TRANSMITTED THROUGH THE PHASE SHIFTERS, THE CROSS-GUIDE COUPLERS, THE COUPLIING MEANS AND THE TRANSMISSION LINE. 